Catalytic carbon fiber preparation methods

ABSTRACT

A method of producing a catalytic carbon fiber may include: oxidizing a virgin carbon fiber to produce an oxidized carbon fiber; reacting the oxidized carbon fiber with a polyamine compound to produce an amine modified carbon fiber; and reacting the amine modified carbon fiber with an organometallic macrocycle to produce the catalytic carbon fiber.

BACKGROUND

Chemical processes often require multiple unit operations to produce aproduct stream. A particular unit operation may be a liquid-liquidcontacting operation whereby two liquids are brought into intimatecontact to effectuate mass transfer between the liquids, a reactionbetween components in the liquids, or both. Another unit operation maybe a gas-liquid contacting operation whereby a gas and a liquid arebrought in contact to effectuate mass transfer between the liquids, areaction between components in the liquids, or both. Liquid-liquidcontacting may be beneficial in some types of chemical reactions whereone reactant is miscible in a first liquid but immiscible in a secondliquid. An example of such a reaction may be where a first reactant ispresent in a polar solvent such as water and a second reactant ispresent in a non-polar solvent such as a hydrocarbon and the water andhydrocarbon are immiscible. Liquid-liquid contacting may have otherapplications such as liquid-liquid extraction whereby a species presentin a first liquid is extracted into a second liquid by mass transferacross the liquid-liquid interface. Gas-liquid contacting may bebeneficial in some types of chemical reactions where a component in thegas phase is to be reacted with a component in the liquid phase of wherea gaseous component is absorbed into the liquid phase.

A particular challenge of liquid-liquid contactors and gas-liquidcontactors, collectively referred to as “mass transfer devices”, may beensuring adequate contact area between phases such that the masstransfer or reactions may occur in an appreciable amount and in aneconomically viable manner. In general, liquid-liquid contactingoperations may be performed with immiscible liquids, such as, forexample, an aqueous liquid and an organic liquid. Using two immiscibleliquids may allow the liquids to be readily separated after theliquid-liquid contacting is completed. However, when a liquid-liquidcontacting operation is performed with immiscible liquids, phaseseparation may occur before adequate contact between the liquids isachieved.

Several mass transfer devices and techniques have been developed toenhance the contact area between phases, including, but not limited to,fiber-bundle type contactors. A fiber-bundle type contactor maygenerally comprise one or more fiber bundles suspended within a shelland two or more inlets where the phases, including gas-liquid orliquid-liquid, may be introduced into the shell. The fiber bundle maypromote contact between the phases by allowing a first phase to flowalong individual fibers of the fiber bundles and a second phase to flowbetween the individual fibers thereby increasing the effective contactarea between the phases. The two phases may flow from an inlet sectionof the shell to an outlet section of the shell while maintainingintimate contact such that a reaction, mass transfer, or both may bemaintained between the two phases.

Fiber-bundle type contactors have been developed to teat mercaptansulfur containing hydrocarbon streams. In these contactors, a liquidcatalyst or solid catalyst bed may be utilized in conjunction withcaustic to convert mercaptan sulfur to disulfide oil. However, thereexist challenges in this process including ensuring that the extent ofreaction is sufficient to such that the resultant product stream is onspecification. Some methods to ensure that the extent of reaction aresufficient to produce a product stream that is on specification may beto design the mass transfer device to have longer contact time bybuilding the mass transfer device physically larger or to design themass transfer device with features that enhance mixing from entranceeffects. While physical features of the mass transfer device may beoptimized to some degree, there may be limitations to the extent towhich a reaction may proceed regardless of the physical configuration ofthe mass transfer device because of limitations of the oxidationcatalyst.

SUMMARY

In an embodiment, a method of producing a catalytic carbon fiber mayinclude: oxidizing a virgin carbon fiber to produce an oxidized carbonfiber; reacting the oxidized carbon fiber with a polyamine compound toproduce an amine modified carbon fiber; and reacting the amine modifiedcarbon fiber with an organometallic macrocycle to produce the catalyticcarbon fiber. In another embodiment, a method of producing a catalyticcarbon fiber may include: oxidizing a virgin carbon fiber to produce anoxidized carbon fiber; reacting an organometallic macrocycle with apolyamine compound to produce an amine modified organometallicmacrocycle; and reacting the oxidized carbon fiber with an aminemodified organometallic macrocycle to produce the catalytic carbonfiber. In another embodiment, a catalytic carbon fiber may include: acarbon fiber, an amine compound covalently bonded to the carbon fiber;and an organometallic macrocycle covalently bonded to the aminecompound.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present disclosure, and should not be used to limit or define thedisclosure.

FIG. 1 is a block flow diagram of a process for producing disulfide oilfrom a hydrocarbon stream containing mercaptan sulfur.

FIG. 2 illustrates a hydrocarbon desulfurization vessel containingcatalytic carbon fibers.

FIG. 3 illustrates a hydrocarbon desulfurization vessel containingcatalytic carbon fibers.

FIG. 4 illustrates a standalone caustic regeneration unit containingcatalytic carbon fibers.

DETAILED DESCRIPTION

The present disclosure may relate to liquid-liquid and gas-liquid masstransfer devices, and in some embodiments, to mass transfer devicescomprising catalytic carbon fibers. Catalytic carbon fibers may comprisean organometallic catalyst that has been chemically grafted onto asurface of a carbon fiber. The catalytic carbon fiber may be used as aheterogeneous catalyst in the liquid-liquid and gas-liquid mass transferdevices.

The catalytic carbon fibers may be prepared by a process comprisingoxidizing a virgin carbon fiber to produce an oxidized carbon fiberfollowed by amine treatment to produce an amine modified carbon fiber.The amine modified carbon fiber may be further reacted with anorganometallic macrocycle to produce the catalytic carbon fiber. Anytype of carbon fiber may be utilized in the present disclosureincluding, but not limited to, carbon fibers prepared usingpolyacrylonitrile (PAN), mesophase pitch, and rayon. Suitable carbonfibers may have any structural ordering including those carbon fibersclassified as turbostratic or graphitic or any structural orderingtherebetween. Carbon fibers may be of any quality including from about50% carbon by weight to about 100% carbon by weight any may have anyclassification such as low modulus carbon fiber having a tensilestrength modulus below 240 million kPa, intermediate modulus carbonfiber having a tensile strength modulus of about 240 million kPa to 500million kPa, or high tensile strength modulus carbon fiber having atensile strength modulus of about 500 million-1.0 billion kPa. Carbonfibers may have any diameter including from about 5 micrometers to about20 micrometers, or any diameters therebetween.

A first step in preparing the catalytic carbon fibers may includeoxidizing a virgin carbon fiber to produce an oxidized carbon fiber.Oxidation may be carried out in a liquid or gas environment to formoxygen-containing functional groups on the surface of the carbon fiber.Oxygen-containing functional groups may include carboxyl, carbonyl,lactone, and hydroxyl which are covalently bonded to at least a portionof the carbon atoms making up the carbon fiber. The step of oxidizingmay oxidize the carbon fiber to any suitable extent. Without limitation,the carbon fiber may be oxidized to include about 0.1 wt. % to about 25wt. % oxygen-containing functional groups. Alternatively, the carbonfiber may be oxidized to include about 0.1 wt. % to about 1 wt. %oxygen-containing functional groups, about 1 wt. % to about 5 wt. %oxygen-containing functional groups, about 5 wt. % to about 10 wt. %oxygen-containing functional groups, about 10 wt. % to about 15 wt. %oxygen-containing functional groups, about 15 wt. % to about 20 wt. %oxygen-containing functional groups, about 20 wt. % to about 25 wt. %oxygen-containing functional groups, or any ranges therebetween. Thedegree of oxidation may be utilized to control the final concentrationorganometallic macrocycle dispersed on the catalytic carbon fiber whichmay in turn directly affect the overall catalytic activity of thecatalytic carbon fiber.

Oxidation of the carbon fiber may be achieved by submersing the virgincarbon fiber in an acid and allowing the acid to react with the virgincarbon fiber. Suitable acids may include mineral acids such ashydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boricacid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodicacid, fluoroantimonic acid, carborane acids, fluoroboric acid,fluorosulfuric acid, hydrogen fluoride, triflic acid, and perchloricacid for example organic acids such as acetic acid, formic acid, citricacid, oxalic acid, and tartaric acid, for example. In addition to, oralternatively to oxidation using acids, the oxidation step may also beperformed using plasma treatment in oxygen atmosphere, gamma radiationtreatment, electrochemical oxidation using a catalyst such as sodiumhydroxide, ammonium hydrogen carbonate, ammonium carbonate, sulfuricacid, or nitric acid, or oxidation by potassium persulfate with sodiumhydroxide or silver nitrate. The acidic oxidation may be performed atany temperature in the range of about 0° C. to 150° C. Alternatively,the oxidation may be performed in a range of 0° C. to about 25° C.,about 25° C. to about 50° C., about 50° C. to about 75° C., about 75° C.to about 100° C., about 100° C. to about 125° C., about 125° C. to about150° C. or any temperature ranges therebetween. Oxidation may beperformed for any period of time suitable for achieving a desiredconcentration of oxygen-containing functional groups on the carbonfibers. The time required to achieve a specified concentration ofoxygen-containing functional groups may be dependent upon many factorsincluding identity and concentration of the acid and temperatureconditions selected. In general, the oxidation may be carried out for aperiod of time ranging from about 1 hour to about 24 hours.Alternatively, the oxidation may be carried out in a time ranging fromabout 1 hour to about 3 hours, about 3 hours to about 6 hours, about 6hours to about 9 hours, about 9 hours to about 12 hour, about 12 hoursto about 15 hours, about 15 hours to about 18 hours, about 18 hours toabout 21 hours, about 21 hours to about 24 hours, or any rangestherebetween. After oxidation by acid treatment, the oxidized carbonfibers may optionally be washed using water or other solvent to removeexcess acid. The oxidized carbon fibers may be dried at elevatedtemperature after washing to remove water or solvent used in the washingstep.

A second step in preparing the catalytic carbon fibers may includeproducing an amine modified carbon fiber. After the oxidized carbonfibers are produced, the oxidized carbon fibers may be reacted with anamine containing compound to produce the amine modified carbon fiber.The amine containing compound may be any polyamine compound containingat least two amine groups including diamines, triamines, and higherorder amines. The amine containing compound may include linear,branched, or cyclic primary or secondary amines, with carbon rangingnumbers from C2-C20. Some specific amine containing compounds mayinclude, without limitation, ethylenediamine, propane-1,3-diamine,butane-1,4-diamine, pentane-1,5-diamine, hexamethylenediamine,diethylenetriamine, benzene-1,3,5-triamine, and combinations thereof.The oxidized carbon fibers may be reacted with the amine containingcompound at any suitable conditions, including at a temperature in therange of about 0° C. to 250° C. Alternatively, the oxidation may beperformed in a range of 0° C. to about 25° C., about 25° C. to about 50°C., about 50° C. to about 75° C., about 75° C. to about 100° C., about100° C. to about 125° C., about 125° C. to about 150° C., about 150° C.to about 175° C., about 175° C. to about 200° C., about 200° C. to about225° C., about 225° C. to about 250° C. or any temperature rangestherebetween. The time required for reacting the oxidized carbon fibersand amine containing compound may be dependent upon many factorsincluding identity of the amine containing compound and temperatureconditions selected. In general, the oxidized carbon fibers may bereacted with the amine containing compound for a period of time rangingfrom about 1 hour to about 24 hours. Alternatively, the oxidized carbonfibers may be carried out in a time ranging from about 1 hour to about 3hours, about 3 hours to about 6 hours, about 6 hours to about 9 hours,about 9 hours to about 12 hour, about 12 hours to about 15 hours, about15 hours to about 18 hours, about 18 hours to about 21 hours, about 21hours to about 24 hours, or any ranges therebetween. After the aminereaction, the amine modified carbon fibers may optionally be washedusing water or other solvent to remove excess amine. The amine modifiedcarbon fibers may be dried at elevated temperature after washing toremove water or solvent used in the washing step.

A third step in preparing the catalytic carbon fibers may includereacting the amine modified carbon fibers with an organometallicmacrocycle to produce the catalytic carbon fiber. Organometallicmacrocycles may include unsubstituted metal phthalocyanines, substitutedmetal phthalocyanines, and combinations thereof. Substituted metalphthalocyanine may include substitutions of halogens, hydroxyl, amine,alkyl, aryl, thiol, alkoxy, nitrosyl groups, or combinations thereof, atone or more peripheral hydrogen atoms on the metal phthalocyanine. Metalphthalocyanines may include any suitable metal including, withoutlimitation, vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), nickel(Ni), copper (Cu), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium(Pd), silver (Ag), and combinations thereof. The organometallicmacrocycle may be dispersed in a solvent including, but not limited towater, pyridine, DMSO, DMF, THF, ethanol, acetonitrile, chloroform,ethylene glycol, methanol, benzene, or combinations thereof prior toreacting with the amine modified carbon fibers.

The amine modified carbon fibers may be reacted with the organometallicmacrocycle at any suitable conditions, including at a temperature in therange of about 0° C. to 150° C. Alternatively, the oxidation may beperformed in a range of 0° C. to about 25° C., about 25° C. to about 50°C., about 50° C. to about 75° C., about 75° C. to about 100° C., about100° C. to about 125° C., about 125° C. to about 150° C. or anytemperature ranges therebetween. The time required for reacting theamine modified carbon fibers and amine containing compound may bedependent upon many factors including identity of the organometallicmacrocycle and temperature conditions selected. In general, the aminemodified carbon fibers may be reacted with the organometallic macrocyclefor a period of time ranging from about 1 hour to about 24 hours.Alternatively, the oxidation may be carried out in a time ranging fromabout 1 hour to about 3 hours, about 3 hours to about 6 hours, about 6hours to about 9 hours, about 9 hours to about 12 hour, about 12 hoursto about 15 hours, about 15 hours to about 18 hours, about 18 hours toabout 21 hours, about 21 hours to about 24 hours, or any rangestherebetween. After the organometallic macrocycle reaction, thecatalytic carbon fiber may optionally be washed using water or othersolvent to remove excess organometallic macrocycle. The catalytic carbonfiber may be dried at elevated temperature after washing to remove wateror solvent used in the washing step.

An alternative synthesis method for producing catalytic carbon fibersmay include reacting an amine containing compound described above withan organometallic macrocycle to produce an amine modified organometallicmacrocycle. The amine modified organometallic macrocycle may then bereacted with and oxidized carbon fibers produced by the same methodsdiscussed above.

Once the catalytic carbon fibers have been synthesized as describedabove, the catalytic carbon fibers may be further processed by shapingthe catalytic carbon fibers. For example, individual strands of thecatalytic carbon fibers may be drawn together and secured to form acatalytic carbon fiber bundle. The catalytic carbon fiber bundle may beutilized in a reactor to form a reaction zone within the reactor.Additional processing of the carbon fibers may include reducing the sizeof the carbon fibers to produce a catalytic carbon fiber suitable forfluidization, for example within a fluidized bed reactor, or may bepelletized or otherwise made suitable for use in a packed bed reactor.

Hydrocarbon streams in refineries and chemical plants often containunwanted contaminants such as organically bound sulfur compounds,carboxylic acids, and hydrogen sulfide. Product specifications may callfor the reduction and/or removal of these contaminants during therefining process. Organically bound sulfur, such as mercaptan sulfur,may be present in some hydrocarbon streams within a refinery or chemicalplant. It may be desirable to reduce the mercaptan sulfur content of ahydrocarbon stream to produce a product stream with reduced mercaptansulfur content. There are generally two options for treating mercaptansulfur containing streams. Mercaptan extraction may be utilized wherebythe mercaptan sulfur is reacted with a caustic stream to produce anorgano-sulfur compound such as a mercaptide. A portion of the mercaptidemay dissolve in the aqueous portion of the caustic stream therebyremoving the mercaptan sulfur from the hydrocarbon stream. In general,the solubility of the organo-sulfur compound is a function of thehydrocarbon chain length whereby relatively lower molecular weightmercaptans may produce a more soluble product when reacted with thecaustic stream and relatively higher molecular weight mercaptans mayproduce a relatively less soluble product when reacted with the causticstream. The organo-sulfur compound may be further oxidized to disulfideoil by reacting the organo-sulfur compound with oxygen in the presenceof a catalyst. For some hydrocarbon streams containing heavier mercaptansulfur containing compounds, mercaptan sweetening may be utilized todirectly convert the mercaptan sulfur to the disulfide oil by reactingthe mercaptan sulfur with oxygen in the presence of a catalyst.Sweetening directly to disulfide oil may be preferable in somehydrocarbon streams where the organo-sulfur compounds produced would berelatively insoluble in the aqueous portion of the caustic stream. Someoperations may involve extraction and sweetening in series whereby amixed hydrocarbon stream containing a portion of relatively lowermolecular weight mercaptan sulfur and a relatively higher molecularweight mercaptan sulfur are contacted with a caustic stream followed byoxidation to produce disulfide oil. Such operations may occur inseparate units or as an integrated process within a single vessel. Anexample of single vessel extraction/oxidation us the Mericat™ II processavailable from Merichem Company.

There may be a wide variety of hydrocarbon streams which containcontaminants that may be removed. While the present application may onlydisclose embodiments with regards to some specific hydrocarbon streams,the disclosure herein may be readily applied to other hydrocarbonstreams not specifically enumerated herein. The caustic treatmentprocess may be appropriate for treatment of any hydrocarbon feedincluding, but not limited to, hydrocarbons such as alkanes, alkenes,alkynes, and aromatics, for example. The hydrocarbons may comprisehydrocarbons of any chain length, for example, from about C₃ to aboutC₃₀, or greater, and may comprise any amount of branching. Someexemplary hydrocarbon feeds may include, but are not limited to, crudeoil, propane, LPG, butane, light naphtha, isomerate, heavy naphtha,reformate, jet fuel, kerosene, diesel oil, hydro treated distillate,heavy vacuum gas oil, light vacuum gas oil, gas oil, coker gas oil,alkylates, fuel oils, light cycle oils, and combinations thereof. Somenon-limiting examples of hydrocarbon streams may include crude oildistillation unit streams such as light naphtha, heavy naphtha, jetfuel, and kerosene, fluidized catalytic cracker or resid catalyticcracker gasoline, or RCC, natural gasoline from NGL fractionation, andgas condensates.

Methods of extracting mercaptan sulfur may include contacting thehydrocarbon stream with a caustic stream containing hydroxide andreacting at least a portion of the mercaptan sulfur content of thehydrocarbon stream with the hydroxide in the caustic stream. Thehydroxide may be any hydroxide capable of reacting with mercaptansulfur. Some exemplary hydroxides may include Group I and Group IIhydroxides such as NaOH, KOH, RbOH, CsOH, Ca(OH)₂, and Mg(OH)₂, forexample. The hydroxide may be present in an aqueous solution in aconcentration suitable for a particular application, generally fromabout 5 wt. % up to and including saturation.

The generalized reaction of hydroxide and mercaptan sulfur is shown inReaction 1 where the mercaptan sulfur (RSH) reacts with hydroxide (XOH),where X is a Group I or Group II cation, to form the correspondingmercaptide (RSX) and water.

RSH+XOH→RSX+H₂O  Reaction 1

As discussed above, depending on the molecular weight of the mercaptansulfur being reacted with the hydroxide, a portion of the mercaptideproduced may dissolve in the aqueous portion of the caustic stream. Oncethe mercaptan sulfur is reacted with the caustic stream, a “spentcaustic” or “rich caustic” solution containing the water, residualhydroxide, and soluble components may be generated. The spent causticmay be regenerated to form lean caustic with reduced mercaptide contentfor recycling back to Reaction 1. One process of regeneration mayinclude mixing oxygen or air with the spent caustic and contacting theresultant mixture with a catalyst to regenerate the caustic stream. Thegeneralized process of regeneration is shown in Reaction 2 where themercaptide (RSX) reacts with water and oxygen in the presence of acatalyst produce disulfide (RSSR), also referred to as disulfide oil(DSO), caustic, and water.

As discussed above, one of the challenges with treatment of mercaptansulfur is that there may be issues with extent of reaction whereby themercaptan sulfur concentration is not reduced to the level required forthe resultant product stream to be on spec. In units which utilize anextractor section and an oxidation section, such as UOP Merox™, thecatalyst may be dispersed in the caustic stream which circulates throughthe extraction and oxidation sections of the unit. In sweetening units,the catalyst may be contained in a fixed bed within a reactor. Thecatalyst may be impregnated in charcoal or activated carbon where thecatalyst bed may be wetted with caustic solution. In either case, thecatalyst may not have enough catalytic activity and/or residence timewithin the reactor may be too short to effectively oxide themercaptides. One of the exemplary uses of the catalytic carbon fibersdisclosed herein is in replacing the conventional oxygenation catalystspresently utilized in the oxidation of mercaptides to produce disulfideoil. As will be discussed in detail below, catalytic carbon fibersexhibit high reactivity to oxidation of mercaptides and have desirablephysical properties which are well suited for use in mercaptideoxidation reactors.

There may be a wide variety of process conditions suitable for oxidationof the mercaptides, the exact conditions of which may vary depending onthe hydrocarbon feed. For lighter hydrocarbons, operating pressure maybe controlled to be slightly above the bubble point to ensureliquid-phase operation. For relatively heavier hydrocarbons, pressuremay be set to keep air dissolved in the oxidation section. Operatingtemperature may also be selected based on the hydrocarbon feed withgeneral conditions of temperature ranging from about 20° C. to about100° C.

FIG. 1 illustrates one embodiment of a hydrocarbon desulfurizationprocess 100 which may utilize catalytic carbon fibers in mercaptideoxidation. In FIG. 1, hydrocarbon feed 102 containing mercaptan sulfurcompounds may be treated in a counter current multiple stage caustictreatment section. Lean caustic 104 may be fed to a last stage 108 wherethe lean caustic extracts the mercaptans from the hydrocarbons enteringlast stage 108 after first being treated in first stage 106. The causticmay be removed from last stage 108 as stream 110 and may be fed to firststage 106 and be contacted with hydrocarbon feed 102. Spent causticstream 112 may be withdrawn from first stage 106 and the treatedhydrocarbon 114 may be withdrawn from last stage 108. The specificdesign of the caustic treatment section is not critical thefunctionality of the catalytic carbon fibers of the present disclosure,however, one design may include staged contactors operating in acounter-current configuration as schematically illustrated in FIG. 1,and another design may be using fiber film liquid-liquid contactor toassist in the mass transfer of the mercaptans from the hydrocarbon feed102 into the caustic treatment solution.

Spent caustic 112 withdrawn from first stage 106 and oxidizer 118 may befed to oxidation section 116. Oxidizer 118 may include any suitableoxidizer, including air, oxygen, hydrogen peroxide, or any other oxygencontaining gas or compound which releases oxygen. Oxidation section 116may include catalytic carbon fibers disclosed herein capable ofoxidizing mercaptides present in spent caustic 112 to form disulfideoil. The mercaptides, water, and oxygen in spent caustic 112 may reactaccording to Reaction 2 in the presence of the catalytic carbon fibersto produce disulfide oil, regenerated caustic, and water. Theregenerated caustic may be drawn off as regenerated caustic stream 118and the disulfide oil may be drawn off as disulfide stream 124. Off-gassteam 126 containing residual gaseous hydrocarbons, air, oxygen, orother gasses may be withdrawn from oxidation section 116 and sent to adownstream unit for further processing or to flare as needed.

As the conditions within oxidation section 116 may be conducive toforming an explosive mixture with combinations of hydrocarbon andoxidizer, it may be desired to operate the oxidation section 116 suchthat the gasses present in oxidation section 116 are below the lowerexplosive limit (LEL) or above the upper explosive limit (UEL). A gasstream 120 may optionally be introduced into oxidation section 116 suchthat the LEL/UEL conditions are maintained. Gas stream 120 may includefuel gas, inert gas, or any other suitable gas to control LEL/UEL.Another alternative may be the inclusion of solvent stream 122 intooxidation section 116. Solvent stream 122 may be from any source butshould preferably contain little to no disulfide oil. Solvent stream 122may be mixed with spent caustic stream 112 prior to entering theoxidation section 116 or it may be injected as a separate stream intothe bottom of oxidation section 116. The solvent may be any lighthydrocarbon or mixture of light hydrocarbons such as naphtha andkerosene that will assist in the separation of the disulfide oil fromthe caustic solution after oxidation of the mercaptans. The disulfideoil may have a higher solubility in the DSO as compared to the aqueousportion of spent caustic 112, with their differential of solubilityproviding an extractive driving force for the DSO. In examples where asolvent is utilized, the solvent may be drawn off with the disulfide oilin disulfide stream 124.

In some examples, regenerated caustic stream 118 may be further purifiedin solvent wash section 128 whereby a solvent stream 130 may contactregenerated caustic stream 118 to further remove DSO from theregenerated caustic stream 118. A Spent caustic stream 132 may bewithdrawn from solvent wash section 128 and additional fresh causticfrom fresh caustic stream 134 may be added to form lean caustic 104.

FIG. 2 illustrates one embodiment of a hydrocarbon desulfurizationvessel 200 containing catalytic carbon fibers described herein. Asillustrated, hydrocarbon desulfurization vessel 200 contains a caustictreatment section 202 containing fiber bundle 204 and an oxidationsection 206 containing catalytic carbon fibers 208. Conduit 210 maycontain caustic treatment section 202 containing fiber bundle 204 whichmay physically separate caustic treatment section 202 from oxidationsection 206 and provide a flow path for fluid to flow through. Oxidationsection 206 containing catalytic carbon fibers 208 may be disposed in anannular space formed between conduit 210 and the walls of vessel 200.

The hydrocarbon feed 212 containing mercaptan sulfur compounds to betreated may be mixed with oxidizer 214 and introduced into conduit 210.In some examples, sparger 218 may be utilized to distribute oxidizer 214into hydrocarbon feed 21. Oxidizer 214 may include any suitableoxidizer, including air, oxygen, hydrogen peroxide, or any other oxygencontaining gas or compound which releases oxygen. Generally, the amountof oxidizer 214 introduced should be sufficient to oxidize all mercaptansulfur compounds present in hydrocarbon feed 212. Once thehydrocarbon/oxidizer feed is introduced into conduit 210, it may flowthrough conduit 210 and contact fiber bundle 204. Caustic stream 220 maybe introduced into conduit 210 such that the hydrocarbon/oxidizer feedmay be mixed with caustic stream 220 before contacting fiber bundle 204.In some examples, it may be desired to disperse the caustic from causticstream 220 to enhance contact between the hydrocarbon phase fromhydrocarbon feed 212 and the aqueous phase from caustic stream 220. Insuch examples, line 222 may be connected to a distributor 224 disposedabove fiber bundle 204 whereby caustic stream 220 is connected todistributor 224 via line 222, and the hydrocarbon/oxidizer feed may mixwith the caustic from caustic stream 220 above fiber bundle 204.

In either example, hydrocarbon/oxidizer feed and caustic from causticstream 220 may contact fiber bundle 204 which may cause the aqueouscaustic to wet the individual fibers of fiber bundle 204. The aqueouscaustic solution will form a film on fibers 204 which will be draggeddownstream through conduit 210 by passage of hydrocarbon through sameconduit. Both liquids may be discharged into separation zone 226 of thevessel 200. The volume of the hydrocarbon will be greater because theaqueous caustic passes through the fiber bundle at a lower volumetricflow rate than the hydrocarbon. During the relative movement of thehydrocarbon with respect to the aqueous caustic film on the fibers, anew interfacial boundary between the hydrocarbon and the aqueous causticsolution is continuously being formed, and as a result fresh aqueouscaustic solution is brought in contact with this surface and allowed toreact with the mercaptan sulfur or other impurities such as phenolics,naphthenic acid and other organic acids in the hydrocarbon. Mercaptansulfur present in the hydrocarbon feed may be reacted with the causticto produce mercaptides as shown in Reaction 1.

In separation zone 226, the aqueous caustic solution and hydrocarbon maycollect in the lower portion of the vessel 200 and separate intohydrocarbon phase 228 and caustic phase 230. The interface 232 withinvessel 200 may be kept at a level above the bottom of the downstream endof fiber bundle 204 so that the aqueous caustic film can be collecteddirectly in the bottom of vessel 200 without it being dispersed into thehydrocarbon phase 228. Most of the phenolate or naphthenate impuritieswhich may cause plugging in a packed bed are thus removed from thehydrocarbon in the caustic phase. Not only does this increase oxidationefficiency but reduces maintenance costs as well. However, someimpurities may remain in the hydrocarbon which may be necessary tofurther treat the with caustic solution in oxidation section 206.Caustic phase 230 may be withdrawn from vessel 200 via pump 234 and maybe returned to conduit 210 via caustic stream 220. The height ofinterface 232 within vessel 200 may be controlled by level controlssystem 236 which may include a level sensor, a level controller, and apurge valve, which may be configured to keep interface 232 at a levelabove the downstream end of fiber bundle 204.

From separation zone 226, hydrocarbon phase 228 may flow upwards intooxidation section 206, whereby the hydrocarbon phase 228 may contactcatalytic carbon fibers 208. Additional caustic, if necessary, may beintroduced into oxidation section 206 via line 238. A distribution gridmay be present in oxidation section 206 which may distribute causticfrom line 238 into oxidation section 206. In oxidation section 206mercaptides, water, and oxygen may react according to Reaction 2 in thepresence of the catalytic carbon fibers to produce disulfide oil,regenerated caustic, and water which may flow upwards through oxidationsection 206. The additional caustic and hydrocarbon may be in contactand in concurrent flow through oxidation section 206. At the upper endof the catalytic carbon fibers, the additional caustic may be separatedfrom the hydrocarbon by a liquid separator device such as chimney typetrays in separation section 240. While chimney type trays areillustrated, there may be many alternative types of liquid separatorscan be used such as overflow weirs, for example. The additionalhydroxide may be collected in separation section 240 and be drawn off asstream 242 to be re-introduced into oxidation section 206. Makeupcaustic 244 may be added intermittently and a caustic purge may beutilized as needed. Hydrocarbon product 246 may be withdrawn from thetop of separation section 240. Off-gas buildup in vessel 200 may bedrawn off through line 248 and be processed in downstream units.

FIG. 3 illustrates another embodiment of a hydrocarbon desulfurizationvessel 300 containing catalytic carbon fibers described herein. FIG. 3illustrates a process conducted in a single vessel where a hydrocarbonfeed 302, oxidizer 304, caustic stream 306, and, optionally, solventstream 308 are introduced into oxidation section 310. Oxidizer 304 mayinclude any suitable oxidizer, including air, oxygen, hydrogen peroxide,or any other oxygen containing gas or compound which releases oxygen.Each of the streams may be introduced into vessel 300 throughdistributor 312 which may distribute the fees into oxidation section310. Oxidation section 310 contains catalytic carbon fibers 314 arrangedto receive the feeds from distributor 312.

In oxidation section 310, the hydrocarbon from hydrocarbon feed 302 andcaustic from caustic stream 306 may contact catalytic carbon fibers 314which may cause the aqueous caustic to wet the individual fibers ofcatalytic carbon fibers 314. The aqueous caustic solution will form afilm on catalytic carbon fibers 314 which will be dragged downstreamthrough oxidation zone 310 by passage of hydrocarbon through vessel 300.During the relative movement of the hydrocarbon with respect to theaqueous caustic film on the fibers, a new interfacial boundary betweenthe hydrocarbon and the aqueous caustic solution is continuously beingformed, and as a result fresh aqueous caustic solution is brought incontact with this surface and allowed to react with the mercaptan sulfuror other impurities such as phenolics, naphthenic acid and other organicacids in the hydrocarbon. Mercaptan sulfur present in the hydrocarbonfeed may be reacted with the caustic to produce mercaptides as shown inReaction 1. The mercaptides produced may further react with oxygenprovided by oxidizer 304 as shown in Reaction 2 in the presence ofcatalytic carbon fibers 314 to produce disulfide oil, regeneratedcaustic, and water.

The oxidation of mercaptides into disulfide oil occurring within theoxidation section 310 may results in a mixture composed of continuousphase caustic, discontinuous phase organic (disulfide oil, and solventif present) droplets dispersed in the caustic phase, and gas (nitrogenand unreacted oxygen from air). The mixture of products, unreactedreactants, and inert species may exit oxidation section 310 and contactfiber bundle 318 and flow into separation section 316. The fiber bundlemay promote phase separation as explained previously. In separationsection 316, the aqueous caustic and hydrocarbon may collect in thelower portion of separation section 316 and separate into hydrocarbonphase 320, caustic phase 322, and gas phase 324. Gas from oxidizer 304disengages from liquid stream at the outlet of fiber bundle 318 andexits through a mist eliminator 326 as off-gas 328. The two immiscibleliquids, as a single stream, flow downwards along fiber bundle 318during which organic hydrocarbon droplets coalesce and form hydrocarbonphase 320, while the aqueous caustic adheres to the fibers and flowsfurther downward to form caustic phase 322.

Hydrocarbon phase 320 containing the hydrocarbons from hydrocarbon feed302 as well as the generated disulfide oil and solvent, if present, maybe withdrawn as stream 330. Caustic phase 322 may contain a residualamount of disulfide oil which may be further reduced before the causticis recycled within vessel 300. Caustic phase 322 may be withdrawn asstream 332 which may be mixed with fresh solvent stream 334 beforecontacting fiber bundle 338 and flowing into separation section 336. Inseparation section 336, the aqueous caustic from caustic phase 322 andsolvent from solvent stream 334 may collect in the lower portion ofseparation section 336 and separate into solvent phase 340 and causticphase 342. Solvent phase 340 may contain the bulk of any residualdisulfide oil present in caustic phase 322 after flowing through fiberbundle 338. Solvent phase 340 may be withdrawn and recycled to vessel300 as solvent stream 308. Caustic phase 342 may be withdrawn andrecycled as stream 344.

FIG. 4 illustrates a standalone caustic regeneration unit 400 comprisingcatalytic carbon fibers 402 disposed in oxidation zone 404. Spentcaustic stream 406 may be mixed with oxidizer 408 and introduced intocaustic regeneration unit 400 through distributor 410. Spent causticstream may be from any unit, including those previously describedherein, which contains a spent caustic and mercaptides. Oxidizer 408 mayinclude any suitable oxidizer, including air, oxygen, hydrogen peroxide,or any other oxygen containing gas or compound which releases oxygen.The mixture of oxidizer 408 and spent caustic stream 406 may contactcatalytic carbon fibers 402 which may cause the aqueous caustic to wetthe individual fibers of catalytic carbon fibers 402. Mercaptidespresent in caustic stream 406 further react with oxygen provided byoxidizer 408 as shown in Reaction 2 in the presence of catalytic carbonfibers 402 to produce disulfide oil, regenerated caustic, and waterwhich may flow upwards along catalytic carbon fibers 402. The resultantdisulfide oil, regenerated caustic, or both may be withdrawn fromregeneration unit 400 as stream 412. Although illustrated in FIG. 4 asone stream, stream 412 may be two or more streams such as in previousfigures where an aqueous phase and oleaginous phase are separatelywithdrawn. Off-gas 414 may also be withdrawn from caustic regenerationunit 400.

Accordingly, the present disclosure may provide methods, systems, andapparatus that may relate to fluid-fluid contacting. The methods,systems. and apparatus may include any of the various features disclosedherein, including one or more of the following statements.

Statement 1. A method of producing a catalytic carbon fiber comprising:oxidizing a virgin carbon fiber to produce an oxidized carbon fiber;reacting the oxidized carbon fiber with a polyamine compound to producean amine modified carbon fiber; and reacting the amine modified carbonfiber with an organometallic macrocycle to produce the catalytic carbonfiber.

Statement 2. The method of statement 1 wherein the step of oxidationcomprises contacting the carbon fiber with an acid selected fromhydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boricacid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodicacid, fluoroantimonic acid, carborane acid, fluoroboric acid,fluorosulfuric acid, hydrogen fluoride, triflic acid, perchloric acid,acetic acid, formic acid, citric acid, oxalic acid, tartaric acid, andcombinations thereof.

Statement 3. The method of statement 2 wherein the step of oxidation isperformed at temperature in a range of about 0° C. to about 150° C.

Statement 4. The method of any of statements 1-3 1 wherein the polyaminecompound comprises a primary or secondary polyamine with a carbon lengthfrom C2-C20.

Statement 5. The method of any of statements 1-4 wherein the polyaminecompound comprises at least one polyamine compound selected fromethylenediamine, propane-1,3-diamine, butane-1,4-diamine,pentane-1,5-diamine, hexamethylenediamine, diethylenetriamine,benzene-1,3,5-triamine, and combinations thereof.

Statement 6. The method of any of statements 1-5 wherein the step ofreacting the oxidized carbon fiber with a polyamine compound isperformed at a temperature in a range of about 0° C. to 250° C.

Statement 7. The method of any of statements 1-6 wherein the step ofreacting the amine modified carbon fiber with an organometallicmacrocycle is performed at a temperature in a range of about 0° C. to150.

Statement 8. The method of any of statements 1-7 wherein theorganometallic macrocycle comprises an unsubstituted metalphthalocyanine a substituted metal phthalocyanine, or combinationsthereof.

Statement 9. The method of statement 8 wherein the substituted metalphthalocyanine is substituted with at least one of a halogen group, ahydroxyl group, an amine group, an alkyl group, an aryl group, a thiolgroup, an alkoxy group, a nitrosyl group, or combinations thereof.

Statement 10 The method of statement 8 wherein the unsubstituted metalphthalocyanine or the substituted metal phthalocyanine comprises a metalselected from vanadium (V), manganese (Mn), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), zinc (Zn), ruthenium (Ru), rhodium (Rh),palladium (Pd), silver (Ag), and combinations thereof.

Statement 11. A method of producing a catalytic carbon fiber comprising:oxidizing a virgin carbon fiber to produce an oxidized carbon fiber;reacting an organometallic macrocycle with a polyamine compound toproduce an amine modified organometallic macrocycle; and reacting theoxidized carbon fiber with an amine modified organometallic macrocycleto produce the catalytic carbon fiber.

Statement 12. The method of statement 11 wherein the step of oxidationcomprises contacting the carbon fiber with an acid selected fromhydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boricacid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodicacid, fluoroantimonic acid, carborane acid, fluoroboric acid,fluorosulfuric acid, hydrogen fluoride, triflic acid, perchloric acid,acetic acid, formic acid, citric acid, oxalic acid, tartaric acid, andcombinations thereof.

Statement 13. The method of any of statements 11-12 wherein polyaminecompound comprises at least one polyamine compound selected fromethylenediamine, propane-1,3 -diamine, butane-1,4-diamine,pentane-1,5-diamine, hexamethylenediamine, diethylenetriamine,benzene-1,3,5-triamine, and combinations thereof.

Statement 14. The method of any of statements 11-13 wherein theorganometallic macrocycle comprises an unsubstituted metalphthalocyanine a substituted metal phthalocyanine, or combinationsthereof.

Statement 15. The method of statement 14 wherein the substituted metalphthalocyanine is substituted with at least one of a halogen group, ahydroxyl group, an amine group, an alkyl group, an aryl group, a thiolgroup, an alkoxy group, a nitrosyl group, or combinations thereof.

Statement 16. The method of statements 14-15 wherein the unsubstitutedmetal phthalocyanine or the substituted metal phthalocyanine comprises ametal selected from vanadium (V), manganese (Mn), iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), zinc (Zn), ruthenium (Ru), rhodium (Rh),palladium (Pd), silver (Ag), and combinations thereof.

Statement 17. A catalytic carbon fiber comprising: a carbon fiber, anamine compound covalently bonded to the carbon fiber; and anorganometallic macrocycle covalently bonded to the amine compound.

Statement 18. The catalytic carbon fiber of statement 17 wherein theamine compound comprises at least one polyamine compound selected fromethylenediamine, propane-1,3-diamine, butane-1,4-diamine,pentane-1,5-diamine, hexamethylenediamine, diethylenetriamine,benzene-1,3,5-triamine, and combinations thereof.

Statement 19. The catalytic carbon fiber of any of statements 17-18wherein the amine compound comprises ethylenediamine.

Statement 20. The catalytic carbon fiber of statement 19 wherein theorganometallic macrocycle comprises a metal phthalocyanine.

EXAMPLES

To facilitate a better understanding of the present disclosure, thefollowing illustrative examples of some of the embodiments are given. Inno way should such examples be read to limit, or to define, the scope ofthe disclosure.

Example 1

In this example, mercaptan oxidation potential of virgin carbon fiberswere evaluated. Kerosene containing 300 ppm of mercaptan sulfur wasprepared. A 3 gram sample of virgin carbon fiber and 150 mL of themercaptan sulfur containing kerosene was mixed vigorously in a shakerbath at 300 RPM and 38° C. Kerosene samples were withdrawn over thecourse of 30 minutes and the mercaptan concentration in each sample wasdetermined by titration. The second order mercaptan oxidation rateconstant was calculated to be 0.22*10⁻⁴ (1/M*min). It was observed thatthe virgin carbon fiber showed little catalytic activity towardmercaptan oxidation.

Example 2

In this example, cobalt phthalocyanine modified carbon fiber wasprepared and the mercaptan oxidation of the modified carbon fiber wasevaluated. A dimethyl sulfoxide (DMSO) solution was prepared by mixing 4g of 4-aminopyridine with 200 mL of DMSO. Thereafter, 4 grams of virgincarbon fiber was measured and added to the DMSO solution and the mixturewas maintained at 80° C. for 22 hours. The carbon fiber was washed withiso-propyl alcohol followed by washing with distilled water and dryingat 60° C. in air. After drying, the carbon fibers were mixed in anaqueous solution containing 1% di-brominated cobalt phthalocyanine atroom temperature for 15 hours. Thereafter, the cobalt phthalocyaninemodified carbon fiber was washed with distilled water and dried at 60°C.

Kerosene containing 300 ppm of mercaptan sulfur was prepared. A 3 gramsample of cobalt phthalocyanine modified carbon fiber from this exampleand 150 mL of the mercaptan sulfur containing kerosene was mixedvigorously in a shaker bath at 300 RPM and 38° C. Kerosene samples werewithdrawn over the course of 30 minutes and the mercaptan concentrationin each sample was determined by titration. The second order mercaptanoxidation rate constant was calculated to be 3.5*10⁻⁴ (1/M*min).

Example 3

In this example, cobalt phthalocyanine modified carbon fiber wasprepared by the methods described above and the mercaptan oxidation ofthe modified carbon fiber was evaluated. 10 g of virgin carbon fiber wasmeasured and added to 175 mL of 70% nitric acid at 80° C. for 5 hours.After nitric treatment, the carbon fibers were washed with distilledwater and thereafter mixed with ethylenediamine at 105° C. for 3 hoursto obtain amine modified carbon fiber. Thereafter, the amine modifiedcarbon fiber was added to a pyridine solution containing 1.3 wt. %di-brominated cobalt phthalocyanine at room temperature for 22 hours.

Kerosene containing 300 ppm of mercaptan sulfur was prepared. A 3 gramsample of the cobalt phthalocyanine modified carbon fiber from thisexample and 150 mL of the mercaptan sulfur containing kerosene was mixedvigorously in a shaker bath at 300 RPM and 38° C. Kerosene samples werewithdrawn over the course of 30 minutes and the mercaptan concentrationin each sample was determined by titration. The second order mercaptanoxidation rate constant was calculated to be 5.45*10⁻⁴ (1/M*min). It wasobserved that the mercaptan oxidation activity was increased by 56%using the amine method for preparing cobalt phthalocyanine modifiedcarbon fiber.

Therefore, the present disclosure is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent disclosure may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the disclosure covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present disclosure. Ifthere is any conflict in the usages of a word or term in thisspecification and one or more patent(s) or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A method of producing a catalytic carbon fibercomprising: oxidizing a virgin carbon fiber to produce an oxidizedcarbon fiber; reacting the oxidized carbon fiber with a polyaminecompound to produce an amine modified carbon fiber; and reacting theamine modified carbon fiber with an organometallic macrocycle to producethe catalytic carbon fiber.
 2. The method of claim 1 wherein the step ofoxidation comprises contacting the virgin carbon fiber with an acidselected from hydrochloric acid, nitric acid, phosphoric acid, sulfuricacid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid,hydroiodic acid, fluoroantimonic acid, carborane acid, fluoroboric acid,fluorosulfuric acid, hydrogen fluoride, triflic acid, perchloric acid,acetic acid, formic acid, citric acid, oxalic acid, tartaric acid, andcombinations thereof.
 3. The method of claim 2 wherein the step ofoxidation is performed at temperature in a range of about 0° C. to about150° C.
 4. The method of claim 1 wherein the polyamine compoundcomprises a primary or secondary polyamine with a carbon length fromC2-C20.
 5. The method of claim 1 wherein the polyamine compoundcomprises at least one polyamine compound selected from ethylenediamine,propane-1,3-diamine, butane-1,4-diamine, pentane-1,5-diamine,hexamethylenediamine, diethylenetriamine, benzene-1,3,5-triamine, andcombinations thereof.
 6. The method of claim 1 wherein the step ofreacting the oxidized carbon fiber with the polyamine compound isperformed at a temperature in a range of about 0° C. to 250° C.
 7. Themethod of claim 1 wherein the step of reacting the amine modified carbonfiber with the organometallic macrocycle is performed at a temperaturein a range of about 0° C. to
 150. 8. The method of claim 1 wherein theorganometallic macrocycle comprises an unsubstituted metalphthalocyanine a substituted metal phthalocyanine, or combinationsthereof.
 9. The method of claim 8 wherein the substituted metalphthalocyanine is substituted with at least one of a halogen group, ahydroxyl group, an amine group, an alkyl group, an aryl group, a thiolgroup, an alkoxy group, a nitrosyl group, or combinations thereof. 10.The method of claim 8 wherein the unsubstituted metal phthalocyanine orthe substituted metal phthalocyanine comprises a metal selected fromvanadium (V), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),copper (Cu), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd),silver (Ag), and combinations thereof.
 11. A method of producing acatalytic carbon fiber comprising: oxidizing a virgin carbon fiber toproduce an oxidized carbon fiber; reacting an organometallic macrocyclewith a polyamine compound to produce an amine modified organometallicmacrocycle; and reacting the oxidized carbon fiber with an aminemodified organometallic macrocycle to produce the catalytic carbonfiber.
 12. The method of claim 11 wherein the step of oxidationcomprises contacting the carbon fiber with an acid selected fromhydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boricacid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodicacid, fluoroantimonic acid, carborane acid, fluoroboric acid,fluorosulfuric acid, hydrogen fluoride, triflic acid, perchloric acid,acetic acid, formic acid, citric acid, oxalic acid, tartaric acid, andcombinations thereof.
 13. The method of claim 11 wherein polyaminecompound comprises at least one polyamine compound selected fromethylenediamine, propane-1,3-diamine, butane-1,4-diamine,pentane-1,5-diamine, hexamethylenediamine, diethylenetriamine,benzene-1,3,5-triamine, and combinations thereof.
 14. The method ofclaim 11 wherein the organometallic macrocycle comprises anunsubstituted metal phthalocyanine a substituted metal phthalocyanine,or combinations thereof.
 15. The method of claim 14 wherein thesubstituted metal phthalocyanine is substituted with at least one of ahalogen group, a hydroxyl group, an amine group, an alkyl group, an arylgroup, a thiol group, an alkoxy group, a nitrosyl group, or combinationsthereof.
 16. The method of claim 14 wherein the unsubstituted metalphthalocyanine or the substituted metal phthalocyanine comprises a metalselected from vanadium (V), manganese (Mn), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), zinc (Zn), ruthenium (Ru), rhodium (Rh),palladium (Pd), silver (Ag), and combinations thereof.
 17. A catalyticcarbon fiber comprising: a carbon fiber, an amine compound covalentlybonded to the carbon fiber; and an organometallic macrocycle covalentlybonded to the amine compound.
 18. The catalytic carbon fiber of claim 17wherein the polyamine compound comprises at least one polyamine compoundselected from ethylenediamine, propane-1,3-diamine, butane-1,4-diamine,pentane-1,5-diamine, hexamethylenediamine, diethylenetriamine,benzene-1,3,5-triamine, and combinations thereof.
 19. The catalyticcarbon fiber of claim 17 wherein the polyamine compound comprisesethylenediamine.
 20. The catalytic carbon fiber of claim 19 wherein theorganometallic macrocycle comprises metal phthalocyanine.